1. Field of the Invention
The present invention relates to semiconductor devices and a manufacturing method thereof, and more particularly, to a semiconductor device having an insulation film on a conductive layer, and a manufacturing method thereof.
2. Description of the Background Art
Reducing the size of interconnections and providing multilayers thereof are now required to further increase the integration density of semiconductor integrated circuit devices. It is necessary to insert an interlayer insulation layer between each interconnection to provide a multilayer structure of the interconnections. If the surface of this interlayer insulation layer is not planar, a stepped portion will be generated at the interconnection formed above the interlayer insulation film. This causes defects such as disconnection.
Therefore, the surface of the interlayer insulation film (the surface of the device) must be made as flat as possible. The technique to planarize the surface of the device is called planarization. This planarization technique has become important in reducing the size and providing multilayers of the interconnection.
An SOG (Spin On Glass) film is known as an interlayer insulation film commonly used in planarization. Research of this SOG film is particularly in progress in the planarization technology taking advantage of fluidity of the material of the interlayer insulation film.
An "SOG film" is a generic term of a film mainly composed of a solution in which a silicon compound is dissolved in an organic solvent, and silicon dioxide (SiO.sub.2) formed from that solution.
In forming an SOG film, first a solution having a silicon compound dissolved in an organic solvent is applied on a substrate in droplets. The substrate is rotated. By this rotation, the solution coating is provided on the substrate formed of interconnections so as to alleviate the stepped portion thereon. More specifically, the coating is formed thick at the concave portion and thin at the convex portion on the substrate. Thus, the solution coating is planarized at the surface.
Heat treatment is then applied to vaporize the organic solvent. Also, polymerization proceeds to result in a planarized SOG film at the surface.
An SOG film is typically classified into an inorganic SOG film that does not include any organic component of a silicon compound, as represented by the following general formula (1), and an organic SOG film including an organic component in a silicon compound, as represented by the following general formula (2). EQU SiO.sub.2 !n (1) EQU R.sub.x SiOy!n (2)
(n, X, Y : integer; R: alkyl group or aryl group)
Inorganic SOG contains a great amount of moisture and a hydroxyl group. The inorganic SOG has a disadvantage that it is more brittle than a silicon oxide film formed by CVD (Chemical Vapor Deposition). For example, a crack is easily generated during heat treatment in an inorganic SOG film when thicker than 0.5 .mu.m.
In contrast, an organic SOG film has the generation of a crack during heat treatment suppressed. The organic SOG film can be formed having a thickness of approximately 0.5-1.0 .mu.m. The usage of an organic SOG film allows the formation of an interlayer insulation film that is greater in film thickness. Therefore, sufficient planarization can be achieved for even a great stepped portion on a substrate.
Although superior in planarization, an inorganic SOG film may adversely affect the metal interconnection and the like since it contains a great amount of moisture and a hydroxyl group. There is a possibility of degradation in the electric characteristics, corrosion, and the like. This problem may similarly be encountered in an organic SOG film including, though smaller in amount than the inorganic SOG film, moisture and a hydroxyl group.
Therefore, when an SOG film is employed as an interlayer insulation film, an insulation film such as a silicon oxide film formed by plasma CVD, for example, having the property of blocking moisture and hydroxyl groups as well as having high insulation and mechanical strength is generally provided above or below the SOG film.
A silicon oxide film formed by plasma CVD is superior in water resistance than an SOG film. However, it was conventionally difficult to obtain satisfactory water resistance effect even when a silicon oxide film formed by plasma CVD is applied. It was therefore difficult to improve reliability of a semiconductor device such as insulation characteristics while also improving planarization in conventional art.